Heretofore, a cathode-ray tube has mainly used as color television picture display apparatus. The cathode-ray tube has considerably large depth in comparison with size of its television picture screen face. Hence it has been impossible to make a flat-type picture display apparatus with such cathode-ray tube. Recently, picture display apparatus of various types, such as an EL(electroluminescence) display device, a plasma display device or a liquid crystal display device etc. have been developed to offer the flat-type picture display apparatus. However, none of them has been able to offer satisfactory performance, such as luminance, contrast, pixel number and color reproducibility.
Then, a flat-type picture display apparatus having high quality performance has been developed by employing electron beams, and such flat-type picture display apparatus is disclosed in the gazette of the Japanese unexamined patent application No. Sho 62-288762 (publication No. Tokkai Hei 1-130453) which was filed by the same assignee as the present invention.
The gazette No. Tokkai Hei 1-130453 discloses that a television picture screen is divided horizontally and vertically into the matrix arrangement of plural small segments, and each of the small segments is scanned by deflecting one electron beam which is separated from the other electron beams. And, fluorescent dots of R(red), G(green) and B(blue) for one picture element in the small segment are shot in turn by the electron beam of which an amount of the irradiation is controlled by color picture signals. As a result, television moving pictures as a whole are reproduced on the television picture screen by arranging all small segments.
FIG.8 is an exploded perspective view showing an internal conventional picture display apparatus. As shown in FIG.8, plural electrodes are stored in an inside space of an enclosure between a front glass plate 8 and a back glass plate 9 as an envelope of the flat-type picture display apparatus. The plural electrodes comprise a back electrode 1, linear cathodes 2a, 2b and 2c as electron beam sources, an electron beam extraction electrode 3, signal electrodes 4, a focusing electrode 5, horizontal deflection electrodes 6 and vertical deflection electrodes 7. And, the inside space of the enclosure between the front glass plate 8 and the back glass plate 9 is evacuated.
The back electrode 1 is made of a flat plate-shaped conductor, and disposed in parallel with the linear cathodes 2a, 2b and 2c.
The plural linear cathodes 2a, 2b and 2c (only 3 pieces are shown in FIG. 8.) are extended in the horizontal direction, and parallelly disposed to each other in the vertical direction so that electron-flow of nearly uniform current-density-distribution is produced in the horizontal direction. These linear cathodes 2a, 2b and 2c are constituted by, for example, coating an oxide cathode material on the surface of tungsten wires.
The electron beam extraction electrode 3, which is made of a conductive plate, is disposed to face the back electrode 1 across the linear cathodes 2a, 2b and 2c. Plural through-holes 10 are formed in the electron beam extraction electrode 3, and aligned in the horizontal direction to have regular intervals to correspond to each linear cathodes 2a, 2b and 2c. Electron streams, which are produced by the linear cathodes 2a, 2b and 2c, are extracted as electron beams in a front direction toward the front glass plate 8 by the potential between the back electrode 1 and the electron beam extraction electrode 3.
The signal electrodes 4 comprises plural oblong conductive plates which are elongated in the vertical direction and aligned in the horizontal direction at predetermined intervals. Plural through-holes 13 are formed in each of the conductive plates at the positions which correspond to the through-holes 10 of the electron beam extraction electrode 3. The through-holes 13 of the signal electrodes 4 are similar in shape to the through-holes 10 of the electron beam extraction electrode 3. The signal electrodes 4 are provided to deflect the electron beams 17 in response to picture signals from external unit, and thereby the electron beams 17 irradiate a definite position of a fluorescent material layer, and the fluorescent material layer emits light of the designated color at a desired luminance.
The focusing electrode 5 is made of a conductive plate and has plural through-holes 14 at the positions which correspond to the through-holes 13 of the signal electrodes 4. The focusing electrode 5 is provided to focus the electron beams 17 at a desired point of the fluorescent material layer.
The horizontal deflection electrodes 6 comprises a pair of conductive plates 16a and 16b having oblong strips elongated in the vertical direction. These oblong strips are disposed to each other on a common plane so that these oblong strips are aligned in parallel with each other in the vertical direction. An aperture between the oblong strips is arranged in parallel with a vertical center line of the through-hole 14 of the focusing electrode 5. The two conductive plates 16a and 16b are used as a pair of the horizontal deflection electrodes 6. The conductive plates 16a, 16b are formed into comb-shaped having comb-teeth parts, respectively. And a pair of the comb-teeth parts are alternatively aligned to face in the vertical direction as shown in FIG.8.
The vertical deflection electrodes 7 comprise a pair of conductive plates 18a and 18b which are formed into a comb-shape, respectively. The conductive plates 18a, 18b are disposed to each other on a common plane so that the conductive plates 18a, 18b are aligned in parallel with each other in the horizontal direction as shown in FIG.8. Respective aperture along with the horizontal line between the conductive plates 18a and 18b is aligned in parallel with a horizontal center line of the through-holes 14 aligned in a line. The conductive plates 18a, 18b are aligned opposing their long horizontal members each other as shown in FIG.8. In other words, two comb-shaped parts of the conducting plates 18a, 18b are mutually engaged keeping an adequate spacing as a pair of the vertical deflection electrodes 7.
A television picture screen 19 is constituted by coating a fluorescent material layer on the inner face of the front glass plate 8, and then by adding a metal-back layer (not shown in the figure). Thereonto, the fluorescent material layer emits light of R(red), G(green) and B(blue) by the irradiation of electron beams 17.
The electron beams 17, which are emitted from the surface of the linear cathodes 2a, 2b and 2c, pass through the through-holes 10 of the electron beam extraction electrode 3, the through-holes 13 of the signal electrode 4 and the through-holes 14 of the focusing electrode 5. And the electron beams 17 collides through the horizontal deflection electrodes 6 and the vertical deflection electrodes 7 with the metal-back layer to make fluorescent material layer emit light.
FIG.9 is a schematic plan view of the television picture screen 19 of the conventional flat-type picture display apparatus as disclosed in Tokkai Hei 1-130453. As shown in FIG.9, the television picture screen 19 has a picture effective area A for displaying a picture by irradiating the electron beams 17 on the television picture screen 19, and a non-picture effective area B which does not display a picture. The non-picture effective area B, which is shown by a crosshatching in FIG.9, is produced on an edge portion of the television picture screen 19. In the picture effective area A of the television picture screen 19, the fluorescent material layer is irradiated by the electron beams 17 to emit light for displaying pictures in the small segment 21. An electron beam passing area E, which is within the picture effective area A, is a portion effectively irradiated by the electron beams 17 having passed through the through-holes 10, 13 and 14 of the plural electrodes 3, 4 and 5, and vertical border lines .alpha. and horizontal border lines .alpha. of the electron beam passing area E are shown with chain lines .alpha. in FIG.9.
Hereinafter, a set of the components for displaying one picture element in the small segment 21 is defined to one unit. Namely, the one unit comprises a part of the back electrode 1, the linear cathode 2a, 2b or 2c, the electron beam extraction electrode 3, the signal electrode 4, the focusing electrode 5, the horizontal deflection electrodes 6 and the vertical deflection electrodes 7 and the television picture screen 19 for displaying one picture element.
In the above-mentioned conventional flat-type picture display apparatus, since it is not necessary for the electron beams 17 to trace in the outside of the electron beam passing area E, a pair of the conductive plates 16a, 16b of the horizontal deflection electrodes 6, a pair of the conductive plates 18a, 18b of the vertical deflection electrodes 7 and the through-hole 14 of the focusing electrode 5 are not provided in the outside of the electron beam passing area E.
However, the above-mentioned conventional flat-type picture display apparatus has different electric fields between the unit for a center portion of the picture effective area A and the unit for an edge portion of the picture effective area A. Therefore, each equipotential surface in the center portion and the edge portion of the picture effective area A has different shape.
FIG. 10 is a cross sectional view showing a part of the horizontal deflection electrodes 6 in the conventional flat-type picture display apparatus. FIG. 11 is an enlarged sectional view of the horizontal deflection electrode of FIG. 10. In the conventional horizontal deflection electrodes 6, the apertures between a pair of the conductive plates 16a and 16b are disposed in the only electron beam passing area E. The end aperture is arranged at the border line .alpha. of the electron beam passing area E. When the electron beams 17 are not deflected by the above-mentioned horizontal deflection electrodes 6, wave-shaped equipotential surface as shown in FIGS. 10 and 11 is produced on the horizontal deflection electrodes 6. The equipotential surface on the edge portion of the electron beam passing area E, that is, the end aperture at the border line a of the electron beam passing area E, has a different formation from the next aperture of the electron beam passing area E as shown in FIG. 11. As mentioned-above, since the equipotential surface has different formations between the edge portion and the center portion, the tracks of the electron beams 17 from the linear cathodes 2a, 2b and 2c vary between the unit in the edge portion and the unit in the center portion. In other words, the track of the electron beams 17 at the border line .alpha. of the electron beam passing area E is not formed to be parallel with the track in the center portion of the television picture screen 19. FIG. 12 is a plan view showing a part of the television picture screen of the conventional flat-type picture display apparatus. As shown in FIG. 12, in the edge portion of the picture effective area A, the electron beams 17 for the adjacent units in the edge portion are mixed and irradiate the television picture screen 19, thereby a brightening portion C and dark portion D comparison with the circumference thereof are produced in the picture effective area A. Accordingly, the conventional flat-type picture display apparatus can not display pictures which have excellent uniformity.
FIG. 13 is a perspective view of the conventional flat-type picture display apparatus. FIG. 14 is a cutaway perspective view showing a part of the conventional flat-type picture display apparatus. As shown in FIGS. 13 and 14, a exhaust pipe 30 and a high voltage terminal 31 are provided on the edge of the front glass plate 8, and further securing screws 32 and plural output terminals for external units are disposed in the space adjacent to the edge of the plane electrodes. Therefore, the electric field distribution in the edge portion of the television picture screen 19 is affected by existence of these devices thereby disturbing the electric field distribution.